Tenascin expression in endomyocardial biopsy specimens in patients with dilated cardiomyopathy: distribution along margin of fibrotic lesions

The prognostic significance of the presence of tenascin-C in patients with stable coronary heart disease

BACKGROUND

We investigated the prognostic value of tenascin-C in patients with stable coronary heart disease.

METHODS

A total of 666 patients were enrolled and followed for 72 months. The primary outcome was a composite of cardiac events. The secondary outcomes were all-cause death, cardiovascular death, acute myocardial infarction (AMI), and heart failure hospitalization.

RESULTS

The area under the curve of tenascin-C to discriminate the occurrence of composite cardiac events was 70 % (95 % CI: 64.2 % to 75.8 %), and the corresponding optimal cutoff value was 19.91 ng/ml. A higher concentration of tenascin-C was associated with a greater risk of composite cardiac events (P trend < 0.001). Similar results were observed in all-cause death, AMI, and heart failure hospitalization.

CONCLUSION

Tenascin-C was found to be an independent predictor of total cardiovascular events in patients with stable coronary heart disease at 72 months, and also for all-cause death, AMI, and heart failure hospitalization.

Tenascin-C in fibrosis in multiple organs: Translational implications

Systemic sclerosis (SSc, scleroderma) is a complex disease with a pathogenic triad of autoimmunity, vasculopathy, and fibrosis involving the skin and multiple internal organs [1]. Because fibrosis accounts for as much as 45% of all deaths worldwide and appears to be increasing in prevalence [2], understanding its pathogenesis and progression is an urgent scientific challenge. Fibroblasts and myofibroblasts are the key effector cells executing physiologic tissue repair on one hand, and pathological fibrogenesis leading to chronic fibrosing conditions on the other. Recent studies identify innate immune signaling via toll-like receptors (TLRs) as a key driver of persistent fibrotic response in SSc. Repeated injury triggers the in-situ generation of "damage-associated molecular patterns" (DAMPs) or danger signals. Sensing of these danger signals by TLR4 on resident cells elicits potent stimulatory effects on fibrotic gene expression and myofibroblast differentiation triggering the self-limited tissue repair response to self-sustained pathological fibrosis characteristic of SSc. Our unbiased survey for DAMPs associated with SSc identified extracellular matrix glycoprotein tenascin-C as one of the most highly up-regulated ECM proteins in SSc skin and lung biopsies [3,4]. Furthermore, tenascin C is responsible for driving sustained fibroblasts activation, thereby progression of fibrosis [3]. This review summarizes recent studies examining the regulation and complex functional role of tenascin C, presenting tenascin-TLR4 axis in pathological fibrosis, and novel anti-fibrotic approaches targeting their signaling.

CpG postconditioning after reperfused myocardial infarction is associated with modulated inflammation, less apoptosis, and better left ventricular function

Postconditioning attenuates inflammation and fibrosis in myocardial infarction (MI). The aim of this study was to investigate whether postconditioning with the cytosine-phosphate-guanine (CpG)-containing Toll-like receptor-9 (TLR9) ligand 1668-thioate (CpG) can modulate inflammation and remodeling in reperfused murine MI. Thirty minutes of left descending coronary artery (LAD) occlusion was conducted in 12-wk-old C57BL/6 mice. Mice were treated with CpG intraperitoneally 5 min before reperfusion. The control group received PBS; the sham group did not undergo ischemia. M-mode echocardiography (3, 7, and 28 days) and Millar left ventricular (LV) catheterization were performed (7 and 28 days) before the hearts were excised and harvested for immunohistochemical (6 h, 24 h, 3 days, 7 days, and 28 days), gene expression (6 h, 24 h, and 3 days; Taqman RT-qPCR), protein, and FACS analysis (24 h and 3 days). Mice treated with CpG showed significantly better LV function after 7 and 28 days of reperfusion. Protein and mRNA expressions of proinflammatory and anti-inflammatory cytokines were significantly induced after CpG treatment. Histology revealed fewer macrophages in CpG mice after 24 h, confirmed by FACS analysis with a decrease in both classically M1- and alternative M2a-monocytes. CpG treatment reduced apoptosis and cardiomyocyte loss and was associated with induction of adaptive mechanisms, e.g., of heme-oxigenase-1 and β-/α-myosin heavy chain (MHC) ratio. Profibrotic markers collagen type Iα (Col-Ια) and Col-III induction was abrogated in CpG mice, accompanied by fewer myofibroblasts. This led to the formation of a smaller scar. Differential matrix metalloproteinase (MMP)/tissue inhibitor of metalloproteinase (TIMP) expression contributed to attenuated remodeling in CpG, resulting in preserved cardiac function in a Toll-like receptor 1- and TLR9-dependent manner. Our study suggests a cardioprotective mechanism of CpG postconditioning, involving Toll-like receptor-driven modulation of inflammation. This is followed by attenuated remodeling and preserved LV function.NEW & NOTEWORTHY Cytosine-phosphate-guanine (CpG) postconditioning seems to mediate inflammation via Toll-like receptor-1 and Toll-like receptor-9 signaling. Enhanced cytokine and chemokine expressions are partly attenuated by IL-10 and matrix metalloproteinase-8 (MMP8) induction, being associated with lower macrophage infiltration and M1-monocyte differentiation. Furthermore, switch from α- to β-MHC and balanced MMP/TIMP expression led to lesser cardiomyocyte apoptosis, smaller scar size, and preserved cardiac function. Data of pharmacological postconditioning have been widely disappointing to date. Our study suggests a new pathway promoting myocardial postconditioning via Toll-like receptor activation.

Tenascin-C aggravates ventricular dilatation and angiotensin-converting enzyme activity after myocardial infarction in mice

AIMS

Tenascin-C (TN-C) is suggested to be detrimental in cardiac remodelling after myocardial infarction (MI). The aim of this study is to reveal the effects of TN-C on extracellular matrix organization and its haemodynamic influence in an experimental mouse model of MI and in myocardial cell culture during hypoxic conditions.

METHODS AND RESULTS

Myocardial infarction was induced in TN-C knockout (TN-C KO) and wild-type mice. Six weeks later, cardiac function was studied by magnetic resonance imaging and under isolated working heart conditions. Myocardial mRNA levels and immunoreactivity of TN-C, TIMP-1, TIMP-3, and matrix metalloproteinase (MMP)-9, as well as serum and tissue activities of angiotensin-converting enzyme (ACE), were determined at 1 and 6 weeks after infarction. Cardiac output and external heart work were higher, while left ventricular wall stress and collagen expression were decreased (P < 0.05) in TN-C KO mice as compared with age-matched controls at 6 weeks after infarction. TIMP-1 expression was down-regulated at 1 and 6 weeks, and TIMP-3 expression was up-regulated at 1 week (P < 0.01) after infarction in knockout mice. MMP-9 level was lower in TN-C KO at 6 weeks after infarction (P < 0.05). TIMP-3/MMP-9 ratio was higher in knockout mice at 1 and 6 weeks after infarction (P < 0.01). ACE activity in the myocardial border zone (i.e. between scar and free wall) was significantly lower in knockout than in wild-type mice 1 week after MI (P < 0.05).

CONCLUSIONS

Tenascin-C expression is induced by hypoxia in association with ACE activity and MMP-2 and MMP-9 elevations, thereby promoting left ventricular dilatation after MI.

Radiotherapy-induced heart disease: a review of the literature

Radiotherapy as one of the four pillars of cancer therapy plays a critical role in the multimodal treatment of thoracic cancers. Due to significant improvements in overall cancer survival, radiotherapy-induced heart disease (RIHD) has become an increasingly recognized adverse reaction which contributes to major radiation-associated toxicities including non-malignant death. This is especially relevant for patients suffering from diseases with excellent prognosis such as breast cancer or Hodgkin's lymphoma, since RIHD may occur decades after radiotherapy. Preclinical studies have enriched our knowledge of many potential mechanisms by which thoracic radiotherapy induces heart injury. Epidemiological findings in humans reveal that irradiation might increase the risk of cardiac disease at even lower doses than previously assumed. Recent preclinical studies have identified non-invasive methods for evaluation of RIHD. Furthermore, potential options preventing or at least attenuating RIHD have been developed. Ongoing research may enrich our limited knowledge about biological mechanisms of RIHD, identify non-invasive early detection biomarkers and investigate potential treatment options that might attenuate or prevent these unwanted side effects. Here, we present a comprehensive review about the published literature regarding clinical manifestation and pathological alterations in RIHD. Biological mechanisms and treatment options are outlined, and challenges in RIHD treatment are summarized.

Histopathological Aspects of the Myocardium in Dilated Cardiomyopathy

Dilated cardiomyopathy is the most common form of cardiac muscle disease, accounting for approximately 60% of all cardiomyopathies. We proposed to identify histopathological changes of the myocardium in dilative cardiomyopathy. This study comprised a total of 19 cases, represented by myocardial fragments from deceased patients with diagnosis of dilated cardiomyopathy. Histopathological analysis allowed changes to be observed for both myocytes and myocardial interstitial components. We have found a combination of hypertrophic, atrophic and normal myocardocytes, or associated with the presence of hydropic changes. We rarely identified the aspect of myocytosis, cytoplasmic accumulation of lipofuscin pigment or mucinous material, and variable nuclear pleomorphism. At the interstitial level we noticed changes in fibrosis, lipomatosis and rarely the presence of inflammatory infiltrate. Histopathological characteristics of the myocardium in dilated cardiomyopathy are numerous but nonspecific, similar to those in the terminal stages of other cardiac diseases.

Comparative mRNA and MicroRNA Profiling during Acute Myocardial Infarction Induced by Coronary Occlusion and Ablation Radio-Frequency Currents

The ligation of the left anterior descending coronary artery is the most commonly used experimental model to induce myocardial infarction (MI) in rodents. A high mortality in the acute phase and the heterogeneity of the size of the MI obtained are drawbacks recognized in this model. In an attempt to solve the problem, our group recently developed a new MI experimental model which is based on application of myocardial ablation radio-frequency currents (AB-RF) that yielded MI with homogeneous sizes and significantly reduce acute mortality. In addition, cardiac structural, and functional changes aroused by AB-RF were similar to those seen in animals with MI induced by coronary artery ligation. Herein, we compared mRNA expression of genes that govern post-MI milieu in occlusion and ablation models. We analyzed 48 mRNAs expressions of nine different signal transduction pathways (cell survival and metabolism signs, matrix extracellular, cell cycle, oxidative stress, apoptosis, calcium signaling, hypertrophy markers, angiogenesis, and inflammation) in rat left ventricle 1 week after MI generated by both coronary occlusion and AB-RF. Furthermore, high-throughput miRNA analysis was also assessed in both MI procedures. Interestingly, mRNA expression levels and miRNA expressions showed strong similarities between both models after MI, with few specificities in each model, activating similar signal transduction pathways. To our knowledge, this is the first comparison of genomic alterations of mRNA and miRNA contents after two different MI procedures and identifies key signaling regulators modulating the pathophysiology of these two models that might culminate in heart failure. Furthermore, these analyses may contribute with the current knowledge concerning transcriptional and post-transcriptional changes of AB-RF protocol, arising as an alternative and effective MI method that reproduces most changes seem in coronary occlusion.

Characteristic adaptations of the extracellular matrix in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a relatively common heart muscle disease characterized by the dilation and thinning of the left ventricle accompanied with left ventricular systolic dysfunction. Myocardial fibrosis is a major feature in DCM and therefore it is inevitable that corresponding extracellular matrix (ECM) changes are involved in DCM onset and progression. Increasing our understanding of how ECM adaptations are involved in DCM could be important for the development of future interventions. This review article discusses the molecular adaptations in ECM composition and structure that have been reported in both animal and human studies of DCM. Furthermore, we provide a transcriptome-based catalogue of ECM genes that are associated with DCM, generated by using NCBI Gene Expression Omnibus database sets for DCM. Based on this in silico analysis, many novel ECM components involved in DCM are identified and discussed in this review. With the information gathered, we propose putative pathways of ECM adaptations in onset and progression of DCM.

Tenascin C upregulates interleukin-6 expression in human cardiac myofibroblasts via toll-like receptor 4

AIM: To investigate the effect of Tenascin C (TNC) on the expression of pro-inflammatory cytokines and matrix metalloproteinases in human cardiac myofibroblasts (CMF).

METHODS: CMF were isolated and cultured from patients undergoing coronary artery bypass grafting. Cultured cells were treated with either TNC (0.1 μmol/L, 24 h) or a recombinant protein corresponding to different domains of the TNC protein; fibrinogen-like globe (FBG) and fibronectin type III-like repeats (TNIII 5-7) (both 1 μmol/L, 24 h). The expression of the pro-inflammatory cytokines; interleukin (IL)-6, IL-1β, TNFα and the matrix metalloproteinases; MMPs (MMP1, 2, 3, 9, 10, MT1-MMP) was assessed using real time RT-PCR and western blot analysis.

RESULTS: TNC increased both IL-6 and MMP3 (P < 0.01) mRNA levels in cultured human CMF but had no significant effect on the other markers studied. The increase in IL-6 mRNA expression was mirrored by an increase in protein secretion as assessed by enzyme-linked immunosorbant assay (P < 0.01). Treating CMF with the recombinant protein FBG increased IL-6 mRNA and protein (P < 0.01) whereas the recombinant protein TNIII 5-7 had no effect. Neither FBG nor TNIII 5-7 had any significant effect on MMP3 expression. The expression of toll-like receptor 4 (TLR4) in human CMF was confirmed by real time RT-PCR, western blot and immunohistochemistry. Pre-incubation of cells with TLR4 neutralising antisera attenuated the effect of both TNC and FBG on IL-6 mRNA and protein expression.

CONCLUSION: TNC up-regulates IL-6 expression in human CMF, an effect mediated through the FBG domain of TNC and via the TLR4 receptor.

Tenascin-C in cardiovascular remodeling: potential impact for diagnosis, prognosis estimation and targeted therapy

Fetal variants of tenascin-C are not expressed in healthy adult myocardium. But, there is a relevant re-occurrence during pathologic cardiac tissue and vascular remodeling. Thus, these molecules, in particular B and C domain containing tenascin-C, might qualify as promising novel biomarkers for diagnosis and prognosis estimation. Since a stable extracellular deposition of fetal tenascin-C variants is present in diseased cardiac tissue, the molecules are excellent target structures for antibody-based delivery of diagnostic (e.g., radionuclides) or therapeutic (bioactive payloads) agents directly to the site of disease. Against the background that fetal tenascin-C variants are functionally involved in cardiovascular tissue remodeling, therapeutic functional blocking strategies could be experimentally tested in the future.

A state of reversible compensated ventricular dysfunction precedes pathological remodelling in response to cardiomyocyte-specific activity of angiotensin II type-1 receptor in mice

Cardiac dysfunction is commonly associated with high-blood-pressure-induced cardiomyocyte hypertrophy, in response to aberrant renin-angiotensin system (RAS) activity. Ensuing pathological remodelling promotes cardiomyocyte death and cardiac fibroblast activation, leading to cardiac fibrosis. The initiating cellular mechanisms that underlie this progressive disease are poorly understood. We previously reported a conditional mouse model in which a human angiotensin II type-I receptor transgene (HART) was expressed in differentiated cardiomyocytes after they had fully matured, but not during development. Twelve-month-old HART mice exhibited ventricular dysfunction and cardiomyocyte hypertrophy with interstitial fibrosis following full receptor stimulation, without affecting blood pressure. Here, we show that chronic HART activity in young adult mice causes ventricular dysfunction without hypertrophy, fibrosis or cardiomyocyte death. Dysfunction correlated with reduced expression of pro-hypertrophy markers and increased expression of pro-angiogenic markers in the cardiomyocytes experiencing increased receptor load. This stimulates responsive changes in closely associated non-myocyte cells, including the downregulation of pro-angiogenic genes, a dampened inflammatory response and upregulation of Tgfβ. Importantly, this state of compensated dysfunction was reversible. Furthermore, increased stimulation of the receptors on the cardiomyocytes caused a switch in the secondary response from the non-myocyte cells. Progressive cardiac remodelling was stimulated through hypertrophy and death of individual cardiomyocytes, with infiltration, proliferation and activation of fibroblast and inflammatory cells, leading to increased angiogenic and inflammatory signalling. Together, these data demonstrate that a state of pre-hypertrophic compensated dysfunction can exist in affected individuals before common markers of heart disease are detectable. The data also suggest that there is an initial response from the housekeeping cells of the heart to signals emanating from distressed neighbouring cardiomyocytes to suppress those changes most commonly associated with progressive heart disease. We suggest that the reversible nature of this state of compensated dysfunction presents an ideal window of opportunity for personalised therapeutic intervention.

Highlighted Article: A novel conditional mouse model was used to investigate early initiating stages of heart disease that are commonly overlooked, and identifies a ‘window of opportunity’ for personalised therapeutic intervention.

Effect of postconditioning on dynamic expression of tenascin-C and left ventricular remodeling after myocardial ischemia and reperfusion

Background

Tenascin-C (TNC), an extracellular matrix glycoprotein, is expressed transiently in distinct areas in association with active tissue remodeling. This study aimed to explore how ischemic postconditioning (PC) affects myocardial expression of TNC and ventricular remodeling using ¹²⁵I-labeled anti-TNC antibody (¹²⁵I-TNC-Ab) in a rat model of ischemia and reperfusion.

Methods

In control rats (n = 27), the left coronary artery (LCA) was occluded for 30 min followed by reperfusion for 1, 3, 7, and 14 days. PC (n = 27) was performed just after the reperfusion. At the time of the study, ¹²⁵I-TNC-Ab (1.0 to 2.5 MBq) was injected. Six to 9 h later, to verify the area at risk, ^99mTc-MIBI (100 to 200 MBq) was injected intravenously just after the LCA reocclusion, with the rats sacrificed 1 min later. Dual tracer autoradiography was performed to assess ¹²⁵I-TNC-Ab uptake and area at risk. To examine the ventricular remodeling, echocardiography was performed 2 M after reperfusion in both groups.

Results

In control rats, ¹²⁵I-TNC-Ab uptake ratio at 1 day after reperfusion was 3.73 ± 0.71 and increased at 3 days (4.65 ± 0.87), followed by a significant reduction at 7 days (2.91 ± 0.55, P < 0.005 vs 3 days) and14 days (2.01 ± 0.17, P < 0.005 vs 1 and 3 days). PC attenuated the ¹²⁵I-TNC-Ab uptake throughout the reperfusion time from 1 to 14 days; 2.59 ± 0.59 at 1 day, P < 0.05: 3.10 ± 0.42 at 3 days, P < 0.005: 1.93 ± 0.37 at 7 days, P < 0.05: 1.40 ± 0.07 at 14 days, P < 0.001. In echocardiography, PC reduced the ventricular end-diastolic and systolic dimensions (1.00 ± 0.06 cm to 0.83 ± 0.14 cm (P < 0.05) and 0.90 ± 0.15 cm to 0.62 ± 0.19 cm (P < 0.05), respectively) and prevented a decline of ventricular percentage fractional shortening (10.5 ± 3.7 to 28.2 ± 10.7, P < 0.005).

Conclusions

These data indicate that ¹²⁵I-TNC-Ab imaging may be a way to monitor myocardial injury, the subsequent repair process, and its response to novel therapeutic interventions like PC by visualizing TNC expression.

Myocardial hypertrophy is associated with inflammation and activation of endocannabinoid system in patients with aortic valve stenosis

AIMS

Endocannabinoids and their receptors have been associated with cardiac adaptation to injury, inflammation and fibrosis. Experimental studies suggested a role for inflammatory reaction and active remodeling in myocardial hypertrophy, but they have not been shown in human hypertrophy. We investigated the association of the endocannabinoid system with myocardial hypertrophy in patients with aortic stenosis.

MAIN METHODS

Myocardial biopsies were collected from patients with aortic stenosis (AS) and atrial myxoma as controls during surgery. Histological and molecular analysis of endocannabinoids and their receptors, inflammatory and remodeling-related cells and mediators was performed.

KEY FINDINGS

Myocardial hypertrophy was confirmed with significantly higher cardiomyocyte diameter in AS than in myxoma patients, which had normal cell size. AS patients presented compensated myocardial adaptation to pressure overload. AS patients had significantly higher: concentration of endocannabinoid anandamide, expression of its degrading enzyme FAAH, and of cannabinoid receptor CB2, being predominantly located on cardiomyocytes. Cell density of macrophages and newly recruited leukocytes were higher in AS group, which together with increased expression of chemokines CCL2, CCL4 and CXCL8, and suppression of anti-inflammatory IL-10 indicates persistent inflammatory reaction. We found higher myofibroblast density and stronger tenascin C staining along with mRNA induction of tenascin C and CTGF in AS patients showing active myocardial remodeling.

SIGNIFICANCE

Our study shows for the first time activation of the endocannabinoid system and predominant expression of its receptor CB2 on cardiomyocytes being associated with persistent inflammation and active remodeling in hypertrophic myocardium of patients with aortic stenosis.

Tenascin-C as Predictor of Left Ventricular Remodeling and Mortality in Patients with Dilated Cardiomyopathy

Background

Several cardiac biomarkers, especially brain natriuretic peptide (BNP) and N-terminal (NT)-proBNP, have been used as predictors of prognosis and negative remodeling in DCM. In the present study, we aimed to evaluate the prognostic value of tenascin-C in dilated cardiomyopathy (DCM) and whether it can be used to determine reverse remodeling in patients with DCM.

Methods

Sixty-six patients with DCM were followed up for 12 months after initiation of medical treatment including carvedilol, ramipril (candesartan if ramipril was not tolerated), spironolactone, and furosemide. Tenascin-C and NT-proBNP measurements and transthoracic echocardiography were performed at baseline and at 12 months.

Results

At 12 months, a significant improvement in New York Heart Association class (2.57 ± 0.6 vs. 1.87 ± 0.5; P < 0.0001), left ventricular end-diastolic volume (217 ± 47 vs 203 ± 48; P < 0.0001), left ventricular ejection fraction (29.1 ± 5.5 vs 30.9 ± 3.8; P < 0.0001), NT-proBNP (2019 ± 558 vs 1462 ± 805; P < 0.0001), and tenascin-C (76 ± 19 vs 48 ± 28; P < 0.0001) values were observed, compared with baseline. Importantly, decrease in tenascin-C values were correlated with increase in left ventricular ejection fraction. Tenascin-C (odds ratio [OR], 1.896; <95% confidence interval [CI], 1.543–2.670; P = 0.02), diabetes mellitus (OR, 2.456; G95% CI, 1.987–3.234; P = 0.01) and hypertension (OR: 2.106, <95% CI, 1.876–2.897; P = 0.03) were independent predictors of mortality in patients with DCM.

Conclusion

Reverse ventricular remodeling obtained with carvedilol, ramipril/candesartan, and spironolacton is associated with decreases in left ventricular end-diastolic volume, left ventricular end-systolic volume, tenascin-C levels, and NT-proBNP levels. Consequently, tenascin-C may be used to evaluate reverse remodeling in patients with DCM.

Atrial natriuretic peptide exerts protective action against angiotensin II-induced cardiac remodeling by attenuating inflammation via endothelin-1/endothelin receptor A cascade

We aimed to investigate whether atrial natriuretic peptide (ANP) attenuates angiotensin II (Ang II)-induced myocardial remodeling and to clarify the possible molecular mechanisms involved. Thirty-five 8-week-old male Wistar-Kyoto rats were divided into control, Ang II, Ang II + ANP, and ANP groups. The Ang II and Ang II + ANP rats received 1 μg/kg/min Ang II for 14 days. The Ang II + ANP and ANP rats also received 0.1 μg/kg/min ANP intravenously. The Ang II and Ang II + ANP rats showed comparable blood pressure. Left ventricular fractional shortening and ejection fraction were lower in the Ang II rats than in controls; these indices were higher (P < 0.001) in the Ang II + ANP rats than in the Ang II rats. In the Ang II rats, the peak velocity of mitral early inflow and its ratio to atrial contraction-related peak flow velocity were lower, and the deceleration time of mitral early inflow was significantly prolonged; these changes were decreased by ANP. Percent fibrosis was higher (P < 0.001) and average myocyte diameters greater (P < 0.01) in the Ang II rats than in controls. ANP decreased both myocardial fibrosis (P < 0.01) and myocyte hypertrophy (P < 0.01). Macrophage infiltration, expression of mRNA levels of collagen types I and III, monocyte chemotactic protein-1, and a profibrotic/proinflammatory molecule, tenascin-C (TN-C) were increased in the Ang II rats; ANP significantly decreased these changes. In vitro, Ang II increased expression of TN-C and endothelin-1 (ET-1) in cardiac fibroblasts, which were reduced by ANP. ET-1 upregulated TN-C expression via endothelin type A receptor. These results suggest that ANP may protect the heart from Ang II-induced remodeling by attenuating inflammation, at least partly through endothelin 1/endothelin receptor A cascade.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Tenascin-C in human cardiac pathology

Tenascin-C (TN-C), a hexameric extracellular matrix glycoprotein, is a pleiotropic regulator of a variety of cell functions associated with embryogenesis, wound healing, cell proliferation, differentiation, motility, and nerve regeneration. Due to its role in remodeling processes, TN-C is involved with many pathologic states including cardiac and vascular diseases as well as inflammation and cancer. Assessment of circulating TN-C may help with identification of heart disease, especially in conjunction other cardiac biomarkers. It may be considered a specific biomarker useful in detecting cardiac pathology, especially in early disease stages and subsequent monitoring of cardiologic therapy. This review will highlight the biochemistry and usefulness of TN-C in clinical laboratory diagnostics to date.

Advances in tenascin-C biology

Tenascin-C is an extracellular matrix glycoprotein that is specifically and transiently expressed upon tissue injury. Upon tissue damage, tenascin-C plays a multitude of different roles that mediate both inflammatory and fibrotic processes to enable effective tissue repair. In the last decade, emerging evidence has demonstrated a vital role for tenascin-C in cardiac and arterial injury, tumor angiogenesis and metastasis, as well as in modulating stem cell behavior. Here we highlight the molecular mechanisms by which tenascin-C mediates these effects and discuss the implications of mis-regulated tenascin-C expression in driving disease pathology.

Matricellular proteins: new molecular targets to prevent heart failure

Matricellular proteins are highly expressed in reparative responses to pressure and volume overload, ischemia, oxidative stress after myocardial injury, and modulate the inflammatory and fibrotic process in ventricular remodeling, which leads to cardiac dysfunction and eventually overt heart failure. Generally, matricellular proteins loosen strong adhesion of cardiomyocytes to extracellular matrix, which would help cells to move for rearrangement and allow inflammatory cells and capillary vessels to spread during tissue remodeling. Among matricellular proteins, osteopontin (OPN) and tenascin-C (TN-C) are de-adhesion proteins and upregulate the expression and activity of matrix metalloproteinases. These matricellular proteins could be key molecules to diagnose cardiac remodeling and also might be targets for the prevention of adverse ventricular remodeling. This review provides an overview of the role of matricellular proteins such as OPN and TN-C in cardiac function and remodeling, as determined by both in basic and in clinical studies.

Dynamic expression of tenascin-C after myocardial ischemia and reperfusion: assessment by 125I-anti-tenascin-C antibody imaging

Tenascin-C, an extracellular matrix glycoprotein, appears only in the early stages of embryonic development. It is not normally expressed in the adult heart but does reappear transiently in distinct areas in association with active tissue remodeling. The aim of this study was to explore serial changes in the expression of tenascin-C after myocardial ischemia and reperfusion, using (125)I-labeled anti-tenascin-C antibody ((125)I-TNC-Ab) in a rat model of acute ischemia and reperfusion.

METHODS

The left coronary artery was occluded for 20 or 30 min, followed by reperfusion for 1, 3, or 7 d in rats with 20 min of ischemia and for 1, 3, 7, 14, or 28 d in rats with 30 min of ischemia. At the time of the study, (125)I-TNC-Ab (1.0-2.5 MBq) was injected. Three to 5 h later, to verify the area at risk, (99m)Tc-methoxyisobutylisonitrile (100-200 MBq) was injected intravenously just after the left coronary artery reocclusion and the rats were sacrificed 1 min later. Dual-tracer autoradiography was performed to assess (125)I-TNC-Ab uptake and the area at risk.

RESULTS

In rats with 20 min of ischemia, (125)I-TNC-Ab uptake peaked at 3 d after reperfusion, followed by faint uptake after 7 d (uptake ratios at 1, 3, and 7 d after reperfusion were 1.81 +/- 0.53, 2.46 +/- 0.79, and 1.23 +/- 0.17, respectively [P < 0.05 vs. 3 d]). In rats with 30 min of ischemia, uptake was high at 1 and 3 d after reperfusion (2.99 +/- 0.90 and 2.71 +/- 0.80, respectively), decreased at 7 and 14 d (1.94 +/- 0.23 and 2.06 +/- 0.37, respectively), and was weak at 28 d (1.47 +/- 0.27, P < 0.005 vs. 1 d, P < 0.05 vs. 3 d).

CONCLUSION

These data indicate that (125)I-TNC-Ab imaging may be a way to monitor myocardial injury and its repair process after ischemia and reperfusion by visualizing tenascin-C expression.

Tenascin-C may aggravate left ventricular remodeling and function after myocardial infarction in mice

Tenascin-C (TN-C) is an extracellular matrix glycoprotein with high bioactivity. It is expressed at low levels in normal adult heart, but upregulated under pathological conditions, such as myocardial infarction (MI). Recently, we (Ref. 34) reported that MI patients with high serum levels of TN-C have a greater incidence of maladaptive cardiac remodeling and a worse prognosis. We hypothesized that TN-C may aggravate left ventricular remodeling. To examine the effects of TN-C, MI was induced by ligating coronary arteries of TN-C knockout (KO) mice under anesthesia and comparing them with sibling wild-type (WT) mice. In WT+MI mice, TN-C expression was upregulated at day 1, peaked at day 5, downregulated and disappeared by day 28, and the molecule was localized in the border zone between intact myocardium and infarct lesions. The morphometrically determined infarct size and survival rate on day 28 were comparable between the WT+MI and KO+MI groups. Echocardiography and hemodynamic analyses demonstrated left ventricular end-diastolic diameter, myocardial stiffness, and left ventricular end-diastolic pressure to be significantly increased in both WT+MI and KO+MI mice compared with sham-operated mice. However, end-diastolic pressure and dimension and myocardial stiffness of KO+MI were lower than those of the WT+MI mice. Histological examination revealed normal tissue healing, but interstitial fibrosis in the residual myocardium in peri-infarcted areas was significantly less pronounced in KO+MI mice than in WT+MI mice. TN-C may thus accelerate adverse ventricular remodeling, cardiac failure, and fibrosis in the residual myocardium after MI.

TGF-beta and fibrosis in different organs - molecular pathway imprints

The action of transforming-growth-factor (TGF)-beta following inflammatory responses is characterized by increased production of extracellular matrix (ECM) components, as well as mesenchymal cell proliferation, migration, and accumulation. Thus, TGF-beta is important for the induction of fibrosis often associated with chronic phases of inflammatory diseases. This common feature of TGF-related pathologies is observed in many different organs. Therefore, in addition to the description of the common TGF-beta-pathway, this review focuses on TGF-beta-related pathogenetic effects in different pathologies/organs, i. e., arthritis, diabetic nephropathy, colitis/Crohn's disease, radiation-induced fibrosis, and myocarditis (including their similarities and dissimilarities). However, TGF-beta exhibits both exacerbating and ameliorating features, depending on the phase of disease and the site of action. Due to its central role in severe fibrotic diseases, TGF-beta nevertheless remains an attractive therapeutic target, if targeted locally and during the fibrotic phase of disease.

Reverse ventricular remodelling after cardiac resynchronization therapy is associated with a reduction in serum tenascin-C and plasma matrix metalloproteinase-9 levels

BACKGROUND

In heart failure patients, cardiac resynchronization therapy (CRT) leads to reverse ventricular remodelling.

AIM

The aim of this study was to evaluate whether changes in levels of circulating biomarkers of extracellular matrix metabolism correlate with the response to CRT.

METHODS AND RESULTS

Clinical parameters, left ventricular (LV) volumes, and circulating levels of tenascin-C (TNC), matrix metalloproteinase-2 (MMP-2), MMP-9, and amino-terminal propeptide of brain natriuretic peptide (NT-proBNP) were assessed in 64 patients at baseline and 6 months follow-up. The majority of patients (72%) showed a >10% reduction in LV end-systolic volume at follow-up, and were classified as responders to CRT. The remaining patients were classified as non-responders. In responders, a significant decrease in circulating levels of TNC (from 60+/-40 ng/mL to 47+/-30 ng/mL, p<0.01), MMP-9 (from 55+/-30 AU to 44+/-27 AU, p<0.01), and NT-proBNP (from 2106+/-1805 pg/mL to 1132+/-1289 pg/mL, p<0.001) were observed at follow-up; MMP-2 levels were unchanged. In non-responders TNC, NT-proBNP, MMP-9 and MMP-2 levels remained unchanged.

CONCLUSION

At 6 months follow-up, CRT was associated with reverse LV remodelling, and a significant decrease in TNC, MMP-9, and NT-proBNP levels. This suggests an important role of ECM modulation in the process of reverse ventricular remodelling in patients responding to CRT.

Higher serum tenascin-C levels reflect the severity of heart failure, left ventricular dysfunction and remodeling in patients with dilated cardiomyopathy

BACKGROUND

Tenascin-C (TN-C), an extracellular matrix glycoprotein, is specifically expressed at high levels during embryonic development, but not in the adult heart. TN-C reappears at sites of inflammatory tissue remodeling or wound healing under various pathologic conditions, such as acute myocardial infarction, acute myocarditis, and some cases of cardiomyopathy. Therefore, the expression of TN-C might be useful for detecting the clinical characteristics of, and ventricular remodeling in, dilated cardiomyopathy (DCM).

METHODS AND RESULTS

Circulating serum TN-C levels in 107 patients with DCM were measured using an ELISA kit. Clinical data were also assessed by Pearson's or Spearman's correlation analysis to estimate correlations between variables. Serum TN-C levels in DCM patients were higher than those in normal controls (p<0.001). TNC levels showed a significantly positive correlation with New York Heart Association functional class (p<0.001), B-type natriuretic peptide level (p<0.001), cardiothoracic ratio on chest X-ray (p<0.01), left ventricular end-diastolic diameter (p<0.05) and left ventricular end-systolic diameter (p<0.01), and a significantly negative correlation with left ventricular ejection fraction (p<0.01).

CONCLUSIONS

The findings suggest that increased serum TN-C levels indicate the severity of heart failure, left ventricular dysfunction and remodeling in patients with DCM.

The mechanistic basis of infarct healing

Myocardial infarction triggers an inflammatory cascade that results in healing and replacement of the damaged tissue with scar. Cardiomyocyte necrosis triggers innate immune mechanisms eliciting Toll-like receptor- mediated responses, activating the complement cascade and generating reactive oxygen species. Subsequent activation of NF-kappaB is a critical element in the regulation of cytokine, chemokine, and adhesion molecule expression in the ischemic myocardium. Chemokine induction mediates leukocyte recruitment in the myocardium. Pleiotropic proinflammatory cytokines, such as TNF-alpha, IL-1, and IL-6, are also upregulated in the infarct and exert a wide range of effects on a variety of cell types. Timely repression of proinflammatory gene synthesis is crucial for optimal healing; IL-10 and TGF-beta-mediated pathways may be important for suppression of chemokine and cytokine expression and for resolution of the leukocytic infiltrate. In addition, TGF-beta may be critically involved in inducing myofibroblast differentiation and activation, promoting extracellular matrix protein deposition in the infarcted area. The composition of the extracellular matrix plays an important role in regulating cell behavior. Both structural and matricellular proteins modulate cell signaling through interactions with specific surface receptors. The molecular and cellular changes associated with infarct healing directly influence ventricular remodeling and affect prognosis in patients with myocardial infarction.

Tenascin-C regulates recruitment of myofibroblasts during tissue repair after myocardial injury

Tenascin-C (TN-C) is an extracellular matrix molecule that is expressed during wound healing in various tissues. Although not detectable in the normal adult heart, it is expressed under pathological conditions. Previously, using a rat model, we found that TN-C was expressed during the acute stage after myocardial infarction and that alpha-smooth muscle actin (alpha-SMA)-positive myofibroblasts appeared in TN-C-positive areas. In the present study, we examined whether TN-C controls the dynamics of myofibroblast recruitment and wound healing after electrical injury to the myocardium of TN-C knockout (TNKO) mice compared with wild-type (WT) mice. In TNKO mice, myocardial repair seemed to proceed normally, but the appearance of myofibroblasts was delayed. With cultured cardiac fibroblasts, TN-C significantly accelerated cell migration, alpha-SMA expression, and collagen gel contraction but did not affect proliferation. Using recombinant fragments of murine TN-C, the functional domain responsible for promoting migration of cardiac fibroblasts was mapped to the conserved fibronectin type III (FNIII)-like repeats and the fibrinogen (Fbg)-like domain. Furthermore, alternatively spliced FNIII and Fbg-like domains proved responsible for the up-regulation of alpha-SMA expression. These results indicate that TN-C promotes recruitment of myofibroblasts in the early stages of myocardial repair by stimulating cell migration and differentiation.

Diagnostic utility of tenascin-C for evaluation of the activity of human acute myocarditis

Tenascin-C (TN-C) is an extracellular matrix protein that is expressed transiently in close association with tissue remodelling in various body sites. In the heart, TN-C is only present during early stages of development, is not expressed in the normal adult, but reappears in pathological states. The purpose of this study was to analyse the expression of TN-C in myocardial tissue from myocarditis patients, and to evaluate the diagnostic value of immunostaining for TN-C in the assessment of inflammatory activity in biopsy specimens. A total of 113 biopsy specimens obtained from 32 patients with a clinical diagnosis of acute myocarditis were examined by immunohistochemistry and in situ hybridization for TN-C. The immunostaining was semi-quantified and compared with histological diagnosis according to the Dallas criteria. Furthermore, serial biopsies from 22 patients were taken during convalescence, and sequential changes in TN-C levels were analysed. Expression of TN-C was specifically detected in endomyocardial biopsy specimens from patients with active-stage inflammation, and disappeared in healed stages. The degree of expression of TN-C correlated with the severity of histological lesions. These data suggest that TN-C reflects disease activity in cases of human myocarditis. Immunostaining for TN-C could enhance the sensitivity and accuracy of diagnosis using biopsy specimens.

Elevated expression of PDGF-C in coxsackievirus B3-induced chronic myocarditis

AIMS

Coxsackievirus B3 (CVB3) is a frequent cause of human chronic myocarditis and subsequent fibrosis, leading to dilated cardiomyopathy. The molecular processes underlying the development of fibrosis are poorly understood. Enhanced levels of platelet-derived growth factors (PDGFs), especially PDGF-C, have recently been linked with the development of different forms of fibrosis. Therefore, the expression of PDGF was analysed in hearts of CVB3-infected major histocompatability complex class II knockout mice. The latter were recently established as mouse model mimicking the chronic inflammation and fibrosis characteristic for this disease.

METHODS AND RESULTS

Expression of PDGF was analysed by reverse transcription-polymerase chain reaction, in situ hybridization, and immunohistochemistry. Hearts of C57BL/6 mice served as controls because infection of these animals leads to acute cardiac inflammation, but the hearts heal without signs of chronic inflammation. In uninfected hearts, basal expression of PDGF, notably PDGF-C, was detectable throughout the heart. The chronic inflammatory process was associated with elevated and sustained expression of all tested PDGF isoforms. Immunostaining and in situ hybridization analysis localized enhanced PDGF levels to areas with highest virus load and inflammatory infiltrations, adjacent to fibrotic areas.

CONCLUSION

PDGF may participate in fibrosis development in CVB3-induced myocarditis. Therefore, PDGF signalling may be considered a target for therapeutic interference.

Circulating tenascin-C levels in patients with idiopathic dilated cardiomyopathy

Circulating serum tenascin-C (an extracellular matrix glycoprotein) levels in patients with idiopathic dilated cardiomyopathy (IDC) were measured. Serum tenascin-C levels were increased in proportion to the severity of left ventricular dysfunction in patients with IDC. The associations of serum tenascin-C levels with serum troponin T and procollagen type III aminoterminal peptide levels suggest that increased levels of serum tenascin-C indicate ongoing replacement fibrosis after myocardial damage in IDC.

Detection of experimental autoimmune myocarditis in rats by 111In monoclonal antibody specific for tenascin-C

BACKGROUND

Although the identification of inflammatory infiltrates in endomyocardial biopsy specimens is necessary for the definite diagnosis of myocarditis, the biopsy test is invasive and is not sensitive. Therefore, a new diagnostic technique for the early and noninvasive evaluation of myocarditis has been awaited. Expression of tenascin-C (TNC), one of the oligometric extracellular glycoproteins, is induced in various pathological states, including inflammation, suggesting that TNC can be a molecular marker of myocarditis.

METHODS AND RESULTS

An 111In anti-TNC monoclonal antibody Fab' fragment was injected intravenously into rats with experimental autoimmune myocarditis (EAM), and the biodistribution of this radiotracer was measured. Rapid clearance of radioactivity from the blood was observed in both EAM and control rats (<1% at 6 hours after injection). Myocardial uptake of the tracer was much higher in EAM rats than in control rats (7.54-, 4.39-, and 3.51-fold at 6, 24, and 48 hours after injection, respectively). By autoradiography, high radioactivities were clearly observed in the regions indicative of inflammation in EAM rats. Single-photon emission CT imaging demonstrated the focal myocardial uptake of 111In anti-TNC Fab' in vivo.

CONCLUSIONS

Radiolabeled anti-TNC Fab' may be useful for the noninvasive diagnosis of myocarditis.

Tenascin-C is a useful marker for disease activity in myocarditis

Tenascin-C (TNC) is an extracellular matrix protein which appears at active sites of tissue remodelling during embryogenesis or cancer invasion. In normal heart, TNC is only present during the early stages of development but reappears in pathological states. This study examined the diagnostic value of TNC for assessing disease activity of myocarditis. Expression of TNC was examined in myosin-induced autoimmune myocarditis mouse models. Sequential changes in amount, localization and the producing cells were analysed by reverse transcriptase-polymerase chain reaction, western blotting, immunohistochemistry and in situ hybridization and compared with the histological picture. The expression of TNC was upregulated at a very early stage of myocarditis. Immunostaining was detectable before cell infiltration and myocytolysis became histologically apparent, remained during the active stage while cell infiltration and necrosis continued, and disappeared in scar tissue with healing. TNC immunostaining was always observed at the periphery of necrotic or degenerating cardiomyocytes in foci of inflammation, the expression level correlating with histological evidence of inflammatory activity. Interstitial fibroblasts were the major source of TNC, expressing the large isoform containing alternative splicing sites. These data demonstrate that TNC is a useful marker for evaluation of disease activity in myocarditis.

Alcoholic cardiomyopathy versus chronic myocarditis--immunohistological investigations with LCA, CD3, CD68 and tenascin

Dilated cardiomyopathy (DCM) is a disorder of unknown aetiology characterized by the left ventricular cavity enlargement and wall thinning associated with reduced left ventricular wall motion. DCM in chronic alcoholics is supposed to be caused by alcohol induced myocardial damage (alcoholic cardiomyopathy). Nevertheless, cardiotropic viruses, such as enteroviruses have long been suspected as causative agents for at least some forms of DCM. In the present study, 13 cases of DCM in chronic alcoholics were investigated with qualification and quantification of infiltrating leucocytes using immunohistological antibodies against leucocyte common antigen (LCA), T-lymphocytes (CD3) and macrophages (CD68). In addition, the expression of tenascin, playing a role in the initiation of fibrotic changes, was examined. All antigens were known to be possibly enhanced in cases of chronic myocarditis. Using these immunohistological techniques, 2 out of 13 cases had evidence for chronic inflammatory myocardial alterations in the sense of lymphocytic infiltrates (>2.0 CD3 T-lymphocytes/visual field at 400 x (HPF); >7 CD3 T-lymphocytes per mm(2)). These cases were diagnosed as having inflammatory cardiomyopathy. The other cases without myocardial inflammation were diagnosed as idiopathic/alcoholic DCM.

Tenascin-C modulates adhesion of cardiomyocytes to extracellular matrix during tissue remodeling after myocardial infarction

Tenascin-C (TNC), an extracellular matrix glycoprotein, plays important roles in tissue remodeling. TNC is not normally expressed in adults but reappears under pathologic conditions. The present study was designed to clarify the contribution of TNC to ventricular remodeling after myocardial infarction. We examined the expression of TNC after experimental myocardial infarction in the rat by immunohistochemistry and in situ hybridization. Within 24 hours of permanent coronary ligation, interstitial fibroblasts in the border zone started to express TNC mRNA. The expression of TNC was down-regulated on Day 7 and was no longer apparent by Day 14 after infarction. During the healing process, TNC protein and TNC-producing cells were found at the edges of the residual myocardium. Some of the TNC-producing cells were immunoreactive for alpha-smooth muscle actin. In culture, TNC increased the number of cardiomyocytes attached to laminin but inhibited the formation of focal contacts at costameres. The results indicate that during the acute phase after myocardial infarction, interstitial cells in the border zone synthesize TNC, which may loosen the strong adhesion of surviving cardiomyocytes to connective tissue and thereby facilitate tissue reorganization.

Extracellular matrix alterations in cardiomyopathy: The possible crucial role in the dilative form

The collagen network, part of the myocardial extracellular matrix (EM), and other EM proteins transmit mechanical forces generated by cardiomyocytes to cardiac cavities. Network rearrangement and enlargement - fibrosis - is an essential component of cardiac remodelling at various pathological stages. In particular, similarly abundant fibrosis occurs in dilated, hypertrophic and restrictive cardiomyopathy, and it is unclear how this relates to respective changes in ventricular cavities and size. Recent studies of hereditary forms have provided evidence that, in hypertrophic cardiomyopathy, the primary changes occur within cardiomyocytes that are subjected to either necrosis or mutations in genes that code for contractile proteins, while gene mutations of EM proteins have not been found. In contrast, in dilative cardiomyopathy, gene mutations of dystrophin, merosin and other proteins connecting the collagen matrix to cardiomyocyte membranes and actin filaments have been found. A distortion of the mechanical link between the contractile apparatus and the collagen matrix may disturb force transmission in both directions and lead to decreased developed pressure and increased end-systolic volume, provoking cardiac dilation. Profound alterations in the EM have also been induced acutely by alcohol, adriamycin or a high pacing rate, resulting in the development of dilative cardiomyopathy. Thus, EM alterations may be the primary factor in the pathogenesis of dilative cardiomyopathy.